1. Field of the Invention
The present invention relates to a thermally powered air diffuser and, more particularly, to a thermally powered variable air volume diffuser that regulates air volume delivery in response to air supply and room air temperature changes.
2. Description of the Prior Art
Numerous types of variable air volume (VAV) systems for controlling room air temperature are known and used, including fan-powered systems, VAV with radiation, VAV with reheat, heat-pump VAV, changeover/bypass VAV, and thermally powered VAV systems. Thermally powered systems typically employ air diffusers having "thermal motors" that open and close internal air flow dampers--so-called "smart diffusers." Thermally powered smart diffusers have several advantages over the equipment comprising other types of VAV systems, including: (1) having self-contained systems for controlling room air supply without the need for dedicated wall and duct thermostats or additional electrical wiring, pneumatic piping, added system pressures; (2) low maintenance requirements and costs; (3) excellent comfort control, due to the fact that temperature control set points may be adjusted at the diffuser itself to provide proportionally modulating control within a restricted temperature span for a particular room or space; (4) reliability, due to a minimum of mechanical components and the entire absence of electrical components; (5) flexibility, allowing walls and partitions to be moved and office space reconfigured without costly reconfiguration of HVAC systems; (6) energy and cost savings, because no energy input is required to drive the system other than that already supplied by the heating and air conditioning system; and (7) low manufacturing and installation costs.
Thermally actuated variable air volume diffusers are well-known in the art. Notable examples include Vance U.S. Pat. No. 4,231,513, issued Nov. 4, 1980, and reissued Jun. 1, 1982, which discloses a diffuser for a conditioned air system for buildings incorporating a self-contained and integrated sensor actuator control system for varying the volume flow of conditioned air through the diffuser in response to changes in room air temperature. The sensor actuator structure for sensing the room air temperature and for modulating the conditioned air flow is entirely contained within the diffuser structure and is powered directly by the changes in room air temperature without auxiliary equipment or power systems. Additionally, Vance teaches a second integrated sensor that measures the temperature of the duct air and provides the actuating force to changeover and convert the operation of the diffuser from a cooling mode to a heating mode, or vice versa.
Brand U.S. Pat. No. 4,491,270 teaches an improvement over Vance. Brand discloses a diffuser comprising four thermal sensor actuators, including a first sensor responsive to changes in the room air temperature when cool air is supplied through the duct into the room. A second thermal sensor actuator is responsive to the duct air and is adapted to engage the first thermal sensor actuator when cool air is supplied through the duct and to disengage the first thermal sensor actuator when warm air is supplied through the duct. A fourth thermal sensor actuator is responsive to changes in the duct air temperature and brings the third thermal sensor actuator into engagement when warm air is supplied through the duct and to disengage the third thermal sensor actuator when cool air is supplied through the duct.
Noll U.S. Pat. No. 4,509,678 discloses a room air diffuser control mechanism which is operated by two thermally powered thermostatic actuator elements, one reacting to the room air temperature and the other reacting to the supply air temperature. When the supply air temperature is cool (e.g., less than 68.degree. F.), the supply air element is retracted and its linkage system rendered inoperative. The room air element, through its linkage system, reacts to control the room temperature by varying the area of an air diffusion discharge opening. When the supply air temperature is warm (e.g., greater than 78.degree. F.), the supply air element reacts to disengage the room air element linkage system and to move the air diffusion discharge opening to an adjustable, predetermined position. In this mode, the room air element does not affect the discharge opening regardless of the temperature of the room air.
Kline et al. U.S. Pat. No. 4,523,713 also teaches an improvement over Vance. However, whereas Brand discloses a diffuser having four thermal sensor actuators, Kline et al teaches a diffuser having three thermal sensor actuators. The first thermal sensor actuator is responsive to changes in the room air temperature and is engaged when cool air is supplied through the duct into the room. A third thermal sensor actuator is responsive to changes in the room air temperature and is engaged when warm air is supplied to the room. A second thermal sensor actuator brings either the first or second thermal sensor actuator into engagement with the diffuser when the appropriate temperature of air is supplied through the duct and disengages the thermal actuator not being used with the duct air temperature.